Lake Cooper Quarry
Research Thesis: The Cambrian Volcanics of Colbinabbin, their
Stratigraphy, Petrology, Geochemistry and Potential as an Ore Forming
Environment.
Jared Broome
B.App.Sci.(Hons) 1992
ABSTRACT
The Lake Cooper Quarry, located within the northern segment of the Heathcote
Greenstone Belt, represents a 275 metre thick sequence of Middle Cambrian
metabasites and interflow sediments.
Metabasites are fine to medium grained (<0.1 - 2.5 mm), subaqueous
lava flows. Primary mineral phases include clinopyroxene and plagioclase.
Secondary minerals are chlorite, epidote, phrenite, pumpellyite, sphene,
calcite and quartz.
The metabasites are low-potassium tholeiites which are chemically similar
to N-type mid-ocean ridge basalts and modern back arc basin tholeiites.
Sea-floor alteration of the metabasites has resulted in the addition of
sodium and the redistribution of calcium. Compared to N-type mid-ocean
ridge basalts, the Lake Cooper Quarry tholeiites have higher silica and
iron values.
The interflow sediments consist of varying amounts of quartz, carbonate
and sulphides (95% pyrite, 3% chalcopyrite and 2% sphalerite). The
sediments have been classified into 3 types:
1. Massive sulphide units
2. Sulphidic argillite units
3. Banded chert and/or carbonate units.
Massive sulphide and sulphidic argillite units are enriched in arsenic
(up to 695ppm), zinc (up to 663ppm) and copper (up to 591ppm).
Sulphur isotope analysis suggests that interflow sediment pyrite formed
at temperatures below 80oC, associated with biogenic reduction of sea-water
sulphate.
Metabasites and interflow sediments represent possible sources for Victorian
turbidite-hosted gold. Evidence such as gold content, veining relationships
and sulphur isotope data favour the metabasites over the interflow sediments
as a possible gold source.
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